Cart wheel with molded bearing components

ABSTRACT

A wheel assembly for a material handling cart includes a spanner bushing having a cylindrical outer surface, a central axis, and an opening through the spanner bushing along the central axis. A bearing has an inner race and an outer race, wherein the inner race surrounds and contacts the cylindrical outer surface of the spanner bushing. A bushing is located adjacent to the bearing, wherein the bushing surrounds and contacts the cylindrical outer surface of the spanner bushing, and the bushing has a non-cylindrical outer surface contour. A hub is centered about the central axis and contacts the outer race of the bearing and the outer surface of the bushing, wherein the bushing rotates with the hub on the cylindrical outer surface of the spanner bushing. Lubricant cavities in the bushing lubricate the bearing and the spanner bushing. Bushing ridges and lips fix the bushing in relation to the hub.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to wheel assemblies for material handling equipment, such as carts, and more particularly to a wheel and hub assembly having a low maintenance ball bearing assembly molded in a hub of a wheel.

[0003] 2. Description of the Prior Art

[0004] Wheels used on devices for material handling have requirements that are increasingly difficult to meet. For example, wheels used on shopping carts are expected to carry larger and larger loads as the large super stores proliferate. It is not uncommon for a shopping cart to be loaded with many cases of paper or canned goods, which can increase the load on the wheels to several hundred pounds. Shopping cart wheels of a generation ago would not be capable of withstanding such loads.

[0005] In bakeries, wheels may be used on racks that are rolled into an oven while food is baked on the rack. Thus, wheels used in baking must withstand high temperatures, without melting or loosing lubrication.

[0006] In addition to withstanding vertical loads, the wheels must withstand an increased lateral load, which may be placed on the wheel as a cart is pushed around a corner or along a surface that is not level.

[0007] Shopping cart wheels should also be designed for economical fabrication, since they are used in very large quantities. Furthermore, high pressure detergent washing is often used to clean shopping carts, and the wheel design should consider cleaning methods that can remove lubricants from wheel bearings, which may lead to noisy or poorly turning wheels.

[0008] Therefore, there is a need for an improved cart wheel that supports heavy loads, that requires little or no maintenance, that protects a bearing from dirt, water, or other corrosive elements, and that rotates smoothly without wobbling.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide an improved wheel and wheel bearing assembly for a material handling cart that is durable, requires less maintenance, is economical to manufacture, is easy to roll, and provides superior vertical and lateral support for heavy loads.

[0010] According to one embodiment of the invention, a wheel assembly for a material handling cart includes a spanner bushing having a cylindrical outer surface, a central axis, and an opening through the spanner bushing along the central axis. A bearing has an inner race and an outer race, wherein the inner race surrounds and contacts the cylindrical outer surface of the spanner bushing. A bushing is located adjacent to the bearing, wherein the bushing surrounds and contacts the cylindrical outer surface of the spanner bushing, and the bushing has a non-cylindrical outer surface contour. A hub is centered about the central axis and contacts the outer race of the bearing and the outer surface of the bushing, wherein the bushing rotates with the hub on the cylindrical outer surface of the spanner bushing. Lubricant cavities in the bushing lubricate the bearing and the spanner bushing. Bushing ridges and lips fix the bushing in relation to the hub.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which like numbers designate like parts, and in which:

[0012]FIG. 1 is a side elevational view of a wheel having a hub assembly in accordance with an embodiment of the present invention;

[0013]FIG. 2 is an exploded view of a wheel having a hub assembly in accordance with the present invention;

[0014]FIG. 3 is a sectional view of a wheel having a hub assembly in accordance with the present invention taken along a line III-III in FIG. 1;

[0015]FIGS. 4 and 5 show, respectively, an inside and outside perspective view of a bushing according to the present invention;

[0016]FIG. 6 is. a side elevational view of an alternate embodiment of a wheel having a hub assembly in accordance with the present invention;

[0017]FIG. 7 is a front sectional view of an alternate embodiment of a wheel having a hub assembly in accordance with the present invention taken along a line VII-VII in FIG. 6;

[0018]FIG. 8 is a side perspective view of a shopping cart having wheel and hub assemblies according to the present invention; and

[0019]FIG. 9 is a schematic side elevational view of a flat cart with the wheel of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] With reference now to the drawings, and in particular with reference to FIG. 1, there is a depicted a side elevational view of a wheel assembly having a bearing assembly in accordance with an embodiment of the present s invention. As shown, wheel assembly 20 includes bearing assembly 22 surrounded by hub 24. Tread 26 may be located about the circumference of hub 24. In the center of wheel assembly 20, axle opening 28 is adapted to receive an axle (not shown). An opening in spanner bushing 30 defines axle opening 28.

[0021] According to one aspect of the present invention, bearing assembly 22 supports vertical and lateral loads which may be placed on the wheel by an axle installed in axle opening 28 of spanner bushing 30. Additionally, bearing assembly 22 holds a lubricant in contact with a bearing and spanner bushing 30, and protects the bearing and spanner bushing 30 from water, detergent, dirt, and other elements that may wear, corrode, or rust the components of bearing assembly 22.

[0022] Referring now to FIG. 2, there is depicted an exploded view of wheel assembly 20 in accordance with the present invention. As shown, hub 24 has tread 26 mounted around its outer rim. The components of bearing assembly 22, which are assembled in the center of hub 24 while it is being fabricated, are shown in an exploded view for a clearer understanding of the relationship of the various components. As illustrated, spanner bushing 30 is tube-like, and includes axle opening 28 for receiving axle 40. Axle 40 is held in place by nut 42.

[0023] Bearing assembly 22 includes bearing 44, bushings 46, and spanner bushing 30. Bearing 44 may be a conventional ball bearing, having inner race 50 and outer race 52. Inner race 50 and outer race 52 provide surfaces for contacting ball bearings 62 and for holding the ball bearings between the two races. (See also FIG. 3, which is a sectional view of wheel assembly 20 taken along line III-III in FIG. 1.)

[0024] In a preferred embodiment, bearing 44 may be implemented with a precision, high-tolerance, sealed ball bearing that is conventional and commercially available. High-tolerance ball bearings may be used to reduce or eliminate wheel wobble, to provide smooth, easy rotation, and to carry heavy loads. Although a ball bearing is preferred, other types of bearings may be used. For example, bearing 44 may be implemented with other types of roller bearings, including cylindrical, spherical, needle, and tapered roller bearings.

[0025] When bearing assembly 22 is assembled, inner race 50 surrounds and contacts the cylindrical outer surface of spanner bushing 30. As wheel assembly 20 rotates and bears a load, inner race 50 will likely remain stationary with respect to spanner bushing 30, while outer race 52 rotates with, and is stationary with respect to, bushings 46 and hub 24.

[0026] Bushings 46 also surround and contact the cylindrical outer surface of spanner bushing 30. As wheel assembly 20 rotates, bushings 46 rotate around, and are in sliding contact with, the cylindrical outer surface of spanner bushing 30.

[0027] Bushings 46 protect bearing 44 from elements that may corrode or impair the operation of bearing 44, and bushings 46 assist in maintaining the position of bearing 44 and spanner bushing 30 as the bushings contact and constrain spanner bushing 30. Moreover, bushings 46 also provide lateral support to bearing 44, and bear some vertical load transferred from axle 40 through spanner bushing 30. Bushings 46 also contain lubricant for the smooth operation of bearing 44, and for lubricating the interface between bushings 46 and spanner bushing 30. Thus, bushings 46 position parts, protect parts, lubricate parts, and assist in bearing the load of the wheel assembly.

[0028] As shown in FIG. 3, bushings 46 are adjacent to, and on either side of, bearing 44. Bushings 46 are preferably generally cylindrically shaped, having a diameter approximately equal to the outer diameter of bearing 44. Bushings 46 are preferably made from polyoxymethylene (POM), or other acetyl plastic material, or other low-friction material.

[0029]FIGS. 4 and 5 show an inside and outside perspective view, respectively, of bushing 46 according to the present invention. As shown, bushing 46 is generally cylindrical, having cylindrical opening 80 that passes all the way through bushing 46 for receiving spanner bushing 30. Opening 80 is defined by inner surface 82, which is designed to surround and contact the cylindrical outer surface of spanner bushing 30. Spanner bushing 30 fits tightly into opening 80, with little or no play, but not tight enough to prevent spanner bushing 30 from smoothly rotating in opening 80.

[0030] Bushings 46 have an inner face 84 and an outer face 86. When the wheel is assembled on a cart, inner face 84 is adjacent to bearing 44, and outer face 86 is adjacent to yoke 76 (See FIG. 3). Outer face 86 is generally round and flat. Outer face 86 can contact yoke 76, with little or no lubrication needed. Outer face 86 may be flush with the material of hub 24, or may extend outward, as shown at bushing extension 54.

[0031] According to an aspect of the present invention, bushings 46 have a non-cylindrical outer surface contour that engages hub 24 in a manner that prevents bushings 46 from moving with respect to hub 24, so that the bushing and the wheel move in unison with respect to each other. Therefore, when hub 24 is assembled, bushings 46 are restricted from moving relative to hub 24 by the features, shapes, or contours of the outer surface of the bushing. Such contours may be ridges, detents, indentations, lobes, fins, fingers, flanges, flutes, splines, projections, and the like.

[0032] In the embodiment shown in greater detail in FIGS. 4 and 5, outer surface 90 of bushings 46 is not cylindrical in that it has ridges 78 or other contours designed to engage or interlock with hub 24 in the area surrounding bearing assembly 22. As may be seen in FIG. 3, ridges 78 extend radially outward from the generally cylindrical outer surface 90 of bushings 46 so that they extend into the body of hub 24. This structure may be made by an injection molding process that injects a plastic material of hub 24 into a mold that surrounds bearing assembly 22. By this manufacturing method, ridges 78 are surrounded by injection molded plastic.

[0033] The purpose of ridges 78 is to secure bushing 46 to hub 24 so that the bushing and the wheel move in unison with respect to each other. In a preferred embodiment, ridges 78 begin near inner face 84 and run parallel to central axis 68 (See FIG. 3), along outer surface 90 toward outer face 86, ending before outer face 86. Ridge faces 94 on the sides of the length of ridges 78 are perpendicular to outer surface 90 to provide structure that engages hub 24 to prevent relative movement between bushings 46 and hub 24.

[0034] In addition to ridges 78, bushings 46 may be prevented from moving axially outward by circumferential lip 92, which runs around the inner edge of outer surface 90. As shown in FIG. 2-5, ridges 78 extend from lip 92 toward outer face 86. Because the smallest diameter of bushings 46 is not toward inner face 84, bushings 46 cannot be removed from hub 24 without breaking or damaging the central portion of hub 24. This design holds bushings 46 captive in the material of hub 24.

[0035] In order to provide low maintenance and smooth rotation, a lubricant is stored within hub assembly 22. In a preferred embodiment shown in FIGS. 3-5, bushings 46 include one or more grooves or lubricant cavities 64 for storing and distributing lubricant 56 over the cylindrical outer surface of spanner bushing 30. Lubricant cavities 64 are located in inner surface 82 of bushing 46, and open to lubricant recess 66. Lubricant distributed on the cylindrical outer surface of spanner bushing 30 lubricates the interface between spanner bushing 30 and inner surface 82 of bushings 46, which contacts spanner bushing 30.

[0036] Additional lubricant may be stored and distributed from lubricant recess 66, which, in a preferred embodiment, is located adjacent to inner race 50 and ball bearings 62, as shown in FIGS. 3 and 4. While lubricant cavities 64 and lubricant recess 66 may or may not be connected, in a preferred embodiment, lubricant cavity 64 and lubricant recess 66 are connected, which simplifies adding lubricant during assembly and enables lubricant stored in either location to be mixed and flow to where it is needed. While lubricant cavities 64 may be open to lubricant recess 66, they are not open to outer face 86. Lubricant recess 66 also permits inner race 50 to rotate without contacting or rubbing bushings 46.

[0037] When wheel assembly 20 is in use, axle 40 is inserted into axle opening 28 in spanner bushing 30. Axle 40 may be implemented with a bolt having head 70 at one end and threads 72 at the other end. Head 70 and nut 42 couple shopping cart yoke 74 and 76 to wheel assembly 20.

[0038] In operation, axle 40, nut 42, and spanner bushing 30 all remain fixed relative to yoke 76.

[0039] Inner face 84 includes outer rim 88, which is designed to contact outer race 52 of bearing 44 and contain lubricant within lubricant recess 66. Thus, bushing 46 and outer race 52 remain fixed relative to each other, while inner race 50 rotates about central axis 68 (See FIG. 3).

[0040] Wheel assembly 20 shown in FIGS. 1-5 is preferably made by an injection molding process that generally injects material around bearing assembly 22, and then uses a second injection molding process to add tread 26 to hub 24.

[0041] The manufacturing process may start with inserting a bushing-bearing-bushing assembly 46, 44, 46 (i.e., bearing assembly 22) into one side of a half-mold of hub 24, wherein the mold of hub 24 is split into two parts by a plane perpendicular to central axis 68. Alternatively, a bushing-bearing 46, 44 may be inserted into one side of the mold, and a second bushing 46 is inserted into the other side, so that when the sides of the mold come together, the bushing-bearing-bushing assembly 46, 44, 46 comes together.

[0042] After inserting bushings 46 and bearing 44 into the half-mold, the mold is closed, forming a mold cavity. Then plastic, such as polypropylene, is injected into the mold cavity. While plastic is being injected, bushings 46 are pressed against bearing 44 to prevent plastic from intruding into bearing 44. Specifically, outer rim 88 of inner face 84 of bushings 46 form a seal with outer race 52 to prevent plastic intrusion. (See FIG. 3) Pressure of the injected plastic against lip 92 helps secure this seal by forcing bushings 46 against bearing 44.

[0043] After a period for solidifying, opening the half-molds, and removing the wheel, the hot wheel may be submerged in a cooling fluid, such as chilled water, to speed cooling. Before submerging in cooling fluid, openings 80 in bushings 46 may be plugged to prevent the fluid from contacting bearing 44.

[0044] Once the wheel has cooled enough, the wheel may be inserted into another mold for forming tread 26 about the outer circumference of wheel 24. Tread 26 is preferably a more pliable plastic than the plastic used for hub 24. As may be seen in FIG. 3, the material of tread 26 may integrally formed with hub 24, wherein tread material passes through openings or holes near the outer circumference of hub 24. Examples of such holes are shown with broken lines, indicating a hidden feature, at holes 32 in FIG. 1. In FIG. 3, it is clear that the material of hub 24 extends radially outward into the tread material, where outer hub edge 60 is shown.

[0045] After molding tread 26 onto hub 24, lubricant is put into lubricant cavities 64 and lubricant recess 66. Finally, spanner bushing 30 is inserted into opening 80, and wheel assembly 20 is ready to be installed on a cart using axle 40 and nut 42.

[0046] By molding bushings 46 in conjunction with bearing 44 into the hub, the bushings serve as lateral extensions of the bearing outer race, distributing the load and minimizing wobble.

[0047] In other embodiments of the present invention, the hub is molded with only bearing 44, while bushings are inserted after molding. This allows the use of plastics with differing thermal characteristics to be used in the hub and the bushings. The bushings may be designed with a smallest diameter located near inner face 84 so that the bushings may be inserted or pressed into place adjacent to the bearing after the wheel has been formed. For example, the embodiment of wheel assembly 100 shown in FIGS. 6 and 7 includes hub 102 and bearing assembly 104. Hub 102 is molded so as to encompass the outer race of bearing 44. This fixes the bearing inside of the hub.

[0048] Bearing assembly 104 includes spanner bushing 30, bearing 44, and bushings 106. Similar to the embodiment shown in FIGS. 1-5, spanner bushing 30 has a central axis 68, and axle opening 28 along central axis 68 through bushing 30. Bearing 44 is also similar to that previously described.

[0049] Bushings 106 are similar to the previous embodiment in that they are adjacent to bearing 44, and contact and surround the cylindrical outer surface of spanner bushing 30 to protect, support, and hold lubricant next to bearing 44 and spanner bushing 30.

[0050] However, bushings 106 are different from the previous embodiment because the smallest diameter of bushings 106 is toward inner face 108, adjacent to bearing 44. This wheel design may be assembled by press fitting bushings 106 into wheel 102 adjacent to bearing 44, which was previously molded into wheel 102. Axial ridges 114 along the non-cylindrical outer surface of bushings 106 may still be used to ensure a strong press fit that will hold bushings 106 fixed in relation to wheel 102 so that the bushing will not move along central axis 68, and will not rotate about central axis 68 relative to wheel 102. The ridges are triangular in transverse cross-section to assist in the press-fit insertion. In addition, bushings 106 have outer lips 116 and outer faces 118 for contacting yoke 76.

[0051] In FIGS. 6 and 7, lubricant cavities 112 may be seen adjacent to, and open to, spanner bushing 30 and bearing 44. Lubricant cavities 110 hold and distribute lubricant to spanner bushing 30 and bearing 44. Although not shown in FIGS. 6 and 7, bushings 106 may include a lubricant recess and a lubricant cavity in a connected configuration similar to that described above. In the present invention, it is important that either lubricant cavities or lubricant recesses distribute lubricant to the cylindrical outer surface of spanner bushing 30 and to parts of bushing 44, such as inner race 50 and ball bearings 62.

[0052] If wheel assembly 100 is used in a high temperature environment, such as on a food handling cart that may be rolled into an oven for baking food items or heat treating other manufactured goods, wheel 102 may not include a tread or tire, and the lubricant used in lubricant cavities or recesses must be able to withstand the temperature without loosing the ability to lubricate or leaking from bearing assembly 104. A high temperature lubricant that may be used in this application.

[0053]FIG. 8 depicts an embodiment of material handling cart in accordance with the present invention. As illustrated, cart 120 includes frame 122, material support structure 124-which may be implemented with a basket, platform, rack, or the like-and wheels 126. Wheels 126 include a spanner bushing, a bearing, first and second bushings, and a hub, as described above in relation to the embodiments shown in FIGS. 1-7. Frame 122 includes vertical and horizontal members that support and bear the load of material placed on material support structure 124, and transfer such load to wheels 126.

[0054] Wheels 126 may or may not be mounted to frame 122 with a swivel mounting, depending upon the application of cart 120. For example, if cart 120 is a shopping cart, the front wheels may swivel, and the back wheels may be mounted in a fixed direction.

[0055]FIG. 9 shows a flat cart 130 having a bed 132, for carrying objects, and a handle 134 for use in pushing or pulling the cart. The cart uses the wheels 20 or 100 of the present invention. The cart is designed to carry heavy loads such as lumber. The wheel of the present invention is well suited to the heavy-duty cart.

[0056] The wheel assembly and bearing assembly of the present invention have the advantages of being easy and inexpensive to manufacture, being nearly maintenance free because the bearing is protected from dirt, water, and other elements, and is permanently lubricated. The width of bearing assembly 22 and 104 provides a stable, smooth-rolling, and strong hub that is able to support heavy loads, in both a vertical direction (perpendicular to central axis 68) and a lateral direction (e.g., a force at the tread parallel to central axis 68).

[0057] The foregoing description of a preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled. 

What is claimed is:
 1. A wheel assembly comprising: a spanner bushing having a cylindrical outer surface, a central axis, and an opening through the spanner bushing along the central axis; a bearing having an inner race and an outer race, wherein the inner race surrounds and contacts the cylindrical outer surface of the spanner bushing; a bushing adjacent to the bearing, the bushing surrounding and contacting the cylindrical outer surface of the spanner bushing, and having a non-cylindrical outer surface contour; and a hub centered about the central axis and contacting the outer race of the bearing and the outer surface of the bushing, wherein the bushing rotates with the hub.
 2. The wheel assembly according to claim 1 further including a second bushing adjacent to the bearing, and surrounding and contacting the cylindrical outer surface of the spanner bushing, wherein the second bushing is on a side of the bearing opposite the bushing.
 3. The wheel assembly according to claim 1 wherein the bushing further includes a lubricant cavity having an opening in an inner surface that surrounds and contacts the cylindrical outer surface of the spanner bushing.
 4. The wheel assembly according to claim 1 wherein the bushing has an inner face adjacent to the bearing, and the inner face further includes a lubricant recess formed in the inner face adjacent to the inner race of the bearing, and wherein the inner face contacts the outer race.
 5. The wheel assembly according to claim 1 wherein the non-cylindrical surface contour of the bushing further includes ridges that extend radially into the hub and extend parallel to the central axis for engaging the hub surrounding the bushing to prevent movement of the bushing with respect to the hub.
 6. The wheel assembly according to claim 6 wherein the ridges on the bushing are adapted to form a press fit joint with the hub.
 7. The wheel assembly according to claim 6 wherein the bushing has an inner face adjacent to the bearing and an outer face opposite the inner face, and wherein the ridges do not extend to the outer face.
 8. The wheel assembly according to claim 1 wherein the bushing further comprises a circumferential lip located adjacent to the bearing, and extending into the hub, the lip preventing the bushing from moving along the central axis with respect to the hub.
 9. The wheel assembly according to claim 1 wherein the bushing comprises a circumferential lip located outside the hub and structured and arranged to be adjacent to a yoke.
 10. A material handling cart comprising: a frame; a material support structure coupled to the frame; a plurality of wheels coupled to the frame, wherein one of the wheels includes: a spanner bushing having a cylindrical outer surface, a central axis, and an opening through the spanner bushing along the central axis; a bearing having an inner race and an outer race, wherein the inner race surrounds and contacts the cylindrical outer surface of the spanner bushing; a bushing adjacent to the bearing, the bushing surrounding and contacting the cylindrical outer surface of the spanner bushing, and having a non-cylindrical outer surface contour; and a hub centered about the central axis and contacting the outer race of the bearing and the outer surface of the bushing, wherein the bushing rotates with the hub.
 11. A method of making a wheel comprising the steps of: locating a bearing along a central axis in the center of a wheel-shaped mold; locating a bushing on each side of the bearing, wherein the bushings are located along the central axis and include axial and circumferential radial extensions; and injecting plastic material into the wheel-shaped mold to produce a wheel, wherein plastic material surrounds the bearing and bushings, and wherein the radial extensions extend into the plastic material.
 12. The method of making a wheel according to claim 11 wherein the bushings have a cylindrical opening through the bushing along the central axis defined by an inner surface, and wherein the bushings include one or more lubrication cavities in the inner surface of the cylindrical opening for containing lubricant.
 13. The method of making a wheel according to claim 11 further including the steps of: placing lubricant in the lubricant cavities; and inserting a spanner bushing in the cylindrical opening.
 14. A method of making a wheel comprising the steps of: locating a bearing along a central axis in the center of a wheel-shaped mold, wherein the bearing includes an outer race; injecting plastic material into the wheel-shaped mold to produce a wheel, wherein plastic material surrounds the bearing and contacts only the outer race; and press fitting a bushing on each side of the bearing, wherein the bushings are located along the central axis and include radial extensions that engage the plastic material.
 15. The method of making a wheel according to claim 14 wherein the bushings have a cylindrical opening through the bushing along the central axis, and wherein the bushings include lubrication cavities in a surface of the cylindrical opening for containing lubricant. 